Rubber compositions for tires comprise in known manner plasticizing agents used for the preparation or synthesis of certain diane elastomers, in order to improve the processability of said compositions in the uncured state and also some of their use properties in the cured state such as, for example, in the case of tire treads, their grip on wet ground or alternatively their resistance to abrasion and to cuts.
For a very long time, it has essentially been highly aromatic oils derived from petroleum, known by the name of DAE oils (for “Distillate Aromatic Extracts”), which have been used to fulfill this plasticizing-agent function. A number of tire manufacturers, for environmental reasons, are today considering gradually replacing these DAE oils by substitution oils of the “non-aromatic” type, in particular by what are called MES oils (for “Medium Extracted Solvates”) or TDAE oils (“Treated Distillate Aromatic Extracts”), which are characterized by a very low content of polyaromatics (approximately 20 to 50 times less).
The Applicants have noted that the replacement, in tire rubber compositions, of the aromatic DAE oils by these MES or TDAE oils was unexpectedly expressed in a reduction in the resistance to abrasion and to cuts of said compositions, this reduction possibly even being crippling for certain applications, in particular with respect to the problem of chipping of tire treads.
“Chipping” (or “scaling”) is a known damage mechanism which corresponds to surface lamellar tears—in the form of chips—of the “rubber” (or rubber composition) which constitutes the treads, under certain aggressive travelling conditions. This problem is encountered in particular on tires for off-road vehicles or vehicles of the site or construction type, which have to travel over different types of ground, some of which are stony and relatively aggressive; it has for example been described, as have some solutions for overcoming it, in patent specifications EP-A-0 030 579 and FR-A-2 080 661 (or GB-A-1 343 487).
Continuing their research, the Applicants have discovered that replacing a portion of these MES or TDAE oils with another specific plasticizing agent not only made it possible to solve the above problem, but, what is even more surprising, also to improve still further the resistance to abrasion and to cuts of the rubber compositions using conventional aromatic oils as plasticizing agents.